The present invention relates to an infrared microscopic/FT-IR (Fourier transform infrared spectrometer) apparatus based on an attenuated total reflection method, in which a surface portion of a sample is analyzed by bringing a prism into press-contact with the surface of the sample, making an infrared light ray incident on the prism at an arbitrary angle, and analyzing the spectrum of the infrared light ray totally reflected from the surface of the sample by the FT-IR apparatus, and a method for analysis of high density recording media using the apparatus.
Magnetic recording media are widely utilized as an audio tape, a video tape, a back-up data cartridge, a floppy disk, and a hard disk. In particular, recently, examination has been actively made to shorten a recording wavelength or realize high density recording by adopting a digital recording method or the like, and it has been required to develop magnetic recording media excellent in electromagnetic transformation characteristic.
With respect to a coating type magnetic recording medium having been mainly used at present, it has been examined to make a magnetic layer thin for reducing a self-demagnetization loss upon recording, thereby improving the electromagnetic transformation characteristic. In recent years, various coating methods have been proposed from the viewpoint of thinning of the magnetic layer.
In general, the surface of a recording medium is smoothened to minimize a spacing loss upon recording/reproducing. In high density recording, since a recording wavelength used is short, recording tends to be affected by the surface roughness, and therefore, the control of the surface roughness is particularly important.
In this way, with increased output of a magnetic tape, it is required to significantly enhance the smoothness of the surface of a magnetic layer, and correspondingly the substantial contact area of the magnetic layer with a sliding member such as a magnetic head or a guide roller becomes large. As a result, the friction coefficient between the magnetic layer and the sliding member becomes large, and thereby an adhesion phenomenon (so-called sticking) therebetween is easy to occur. This causes a problem such as the lack of running characteristic and durability of the magnetic tape.
To solve the above problem, it has been examined to use various organic lubricants. For example, attempts have been made to add higher fatty acid or its ester in or on the magnetic layer of the magnetic recording medium for reducing the friction coefficient between the magnetic layer and the sliding member.
At the present time, however, as a method of quantitatively measuring the amount of lubricant adhering on the surface of the magnetic recording medium or contained in the medium, there has been known only a method of analyzing the amount of the lubricant by extracting the lubricant by. using solvent. According to such an extraction method, only a lubricant dissolved in a solvent (hexane or toluene) can be measured, and it takes a lot of time to measure the amount of the lubricant. For this reason, it has been very difficult to control the added amount of a lubricant in the production process for a magnetic recording medium.
On the other hand, in a magnetic recording apparatus, typically a hard disk, mainly including a recording/reproducing magnetic head and a magnetic recording medium, a friction force occurs between the magnetic head and the magnetic recording medium, thereby causing wear of the magnetic head and the magnetic recording medium. If the wear reaches a magnetic layer of the magnetic recording medium, there occurs a so-called head crush phenomenon in which information recorded in the recording layer is crushed, and accordingly, to ensure the reliability of the magnetic recording apparatus, it is important to prevent the above-mentioned head crush phenomenon.
To prevent the head crush phenomenon, it is required to improve the wear resistance of a magnetic recording medium itself. In general, to achieve such a purpose, a magnetic layer is covered with a protective layer made from carbon, an oxide, a carbide, or a nitride and further a lubricating film is formed on the protective layer. The lubricating film generally requires characteristics such as a low surface energy, heat resistance, chemical stability and lubricity. At present, a perfluoroalkylpolyether or a perfluoroalkyl compound disclosed in U.S. Pat. No. 3,778,308 has been most extensively used as a compound for forming the lubricating film.
In a magnetic recording apparatus having been mainly used at present, recording/reproducing is performed in a state in which a specific gap is kept between a magnetic head and the surface of a magnetic recording medium. Such a specific gap is called a floating amount. To enhance the recording density to the magnetic recording medium, it is required to make small the floating amount of the magnetic head. In recent years, as the recording density of a magnetic recording apparatus becomes significantly higher, the floating amount becomes smaller. Further, as the ultimate recording method, in recent years, there has been proposed a so-called contact recording method in which recording/reproducing is performed with the floating amount set to zero, that is, in a state in which a magnetic head is usually in contact with the surface of a magnetic recording medium.
In this way, as the floating amount of a magnetic head becomes smaller, a period of time in which the magnetic head is slid in contact with the surface of a magnetic recording medium becomes necessarily larger, and therefore, it is required to reduce the dynamic friction coefficient and wear by enhancing the continuously sliding durability of a lubricating film. Further, in a magnetic recording apparatus.operated in accordance with the extremely low floating method or contact recording method, since the surface roughness and waviness of a magnetic recording medium becomes smaller, a higher maximum static friction force (adhesion) is easy to occur between the magnetic head and the magnetic recording medium. The adhesion may cause the impossible starting of the magnetic recording medium or damage of the magnetic head.
The thickness of a lubricating film present on the surface of the magnetic recording medium is one major cause of occurrence of adhesion. The amount of the lubricant present on the magnetic recording medium is quantitatively measured, for example, by using an ellipsometer or in accordance with XPS (X-ray photoelectron spectroscopy). In the case of the method using the ellipsometer, since the measured result is largely affected by the surface roughness of the magnetic recording medium, it is difficult to accurately measure the amount of the lubricant. In the case of XPS, since the measurement is performed in vacuum, the lubricant on the surface of the magnetic recording medium is lost, and since the measurement is performed by using fluorine atoms, it is impossible to suitably measure a hydrocarbon based lubricant.
With respect to an optical disk (phase change type or magneto-optical type), a spacing between a conventional disk and the optical head is in a range of several hundred nm to several xcexcm, which spacing is considerably larger than the spacing adopted for other magnetic recording methods. Accordingly, a protective film having about several hundred xcexcm is formed on a recording layer of the optical disk. In this way, since the conventional optical disk has a large spacing, a protective film having a large thickness can be formed on the recording layer, with a result that there is a sufficient margin to take a tribological characteristic into account.
In the case of optical recording performed in a near field, which is being studied and developed at present, however, a spacing between a recording layer and an optical head may be considered to be 100 xcexcm or less, and therefore, the thickness of a protective layer must be several ten nm or less. In this case, the tribological characteristic required for optical recording in the near field is little different from that required for the existing magnetic disk or the like. It may be considered that the surface of the optical disk be coated with an organic thin film as a lubricant layer to about several nm. Accordingly, even for the optical disk, it is required to examine the amount and orientation of a lubricating film on the optical disk just as the magnetic disk or the like.
As described above, the qualitative analysis and quantitative analysis of a lubricant on or in a medium have been based on element analysis such as XPS; however, since the element analysis is generally performed in vacuum, there is a possibility that the lubricant is evaporated. Further, since carbon atoms and hydrogen atoms are usually present as contaminants on the surface of the medium, they cannot be discriminated from the lubricant. Accordingly, only in the case where fluorine atoms are contained in the lubricant, the amount of the lubricant can be measured on the basis of the amount of fluorine atoms.
In general, not only perfluoropolyether or a perfluoroalkyl compound containing fluorine atoms but also hydrocarbon based fatty acid or fatty acid ester is used as a lubricant compound. Accordingly, the above method cannot be applied to analysis of all of the lubricant compounds. Further, in a high sensitivity reflected infrared absorption spectroscopy, since absorption of a non-magnetic supporting body cannot be sufficiently removed, the spectrum of the non-magnetic supporting body is superimposed to the spectrum of a lubricant adhering thereon, with a result that it is very difficult to discriminate only the spectrum of the lubricant.
An object of the present invention is to provide an optical analysis apparatus, more specifically, an infrared microscopic/FT-IR apparatus capable of simply, accurately performing qualitative analysis and quantitative analysis of an organic thin film on a high density recording medium and an organic material in the medium, and an analysis method for the high density recording medium using the apparatus.
According to a first aspect of the present invention, there is provided an infrared microscopic/FT-IR (Fourier transform infrared spectrometer) apparatus based on an attenuated total reflection method, the apparatus including: a semi-spherical prism having a smooth, flat bottom surface; and an incident angle variable optical system in which a sample mounting portion is separated from an incident optical system by the semi-spherical prism; whereby a surface portion of a sample is analyzed by bringing the prism in press-contact with the surface of the sample, making an infrared light ray incident on the prism at a specific angle, and analyzing the spectrum of the infrared light ray totally reflected from the surface of the sample by the FT-IR apparatus.
The above incident angle variable optical system may be housed in an enclosed sample chamber.
The above incident angle variable optical system may include parabolic mirrors opposed to each other.
The above apparatus may further includes a contact pressure control means for finely adjusting a contact pressure applied from the surface of the sample to the bottom surface of the semi-spherical prism.
According to a second aspect of the present invention, there is provided an infrared microscopic/FT-IR apparatus based on an attenuated total reflection method, the apparatus including: a semi-spherical prism having a smooth, flat bottom surface; and a contact pressure control means for finely adjusting a contact pressure applied from the surface of the sample to the bottom surface of the semi-spherical prism; whereby a surface portion of a sample is analyzed by bringing the prism in press-contact with the surface of the sample, making an infrared light ray incident on the prism at a specific angle, and analyzing the spectrum of the infrared light ray totally reflected from the surface of the sample by the FT-IR apparatus.
According to a third aspect of the present invention, there is provided a method for carrying out at least one of qualitative analysis and quantitative analysis for a surface portion of a recording medium, including the steps of: preparing an infrared microscopic/FT-IR apparatus based on an attenuated total reflection method, the apparatus including a semi-spherical prism having a smooth, flat bottom surface, and an incident angle variable optical system in which a sample mounting portion is separated from an incident optical system by the semi-spherical prism; bringing the prism in press-contact with the surface of the sample; making an infrared light ray incident on the prism at a specific angle; and analyzing the spectrum of the infrared light ray totally reflected from the surface of the sample by the FT-IR apparatus.
According to a fourth aspect of the present invention, there is provided a method for carrying out at least one of qualitative analysis and quantitative analysis for a surface portion of a recording medium, including the steps of: preparing an infrared microscopic/FT-IR apparatus based on an attenuated total reflection method, the apparatus including a semi-spherical prism having a smooth, flat bottom surface, and a contact pressure control means for finely adjusting a contact pressure applied from the surface of the sample to the bottom surface of the semi-spherical prism; bringing the prism in press-contact with the surface of the sample; making an infrared light ray incident on the prism at a specific angle; and analyzing the spectrum of the infrared light ray totally reflected from the surface of the sample by the FT-IR apparatus.
In the above method, the recording medium may be a coating type magnetic recording medium in which a magnetic layer is formed on a non-magnetic supporting body by a coating film mainly containing a ferromagnetic powder and a binder and additionally containing an organic lubricant.
In the above method, preferably, the recording medium may be a metal thin film type magnetic recording medium in which a metal thin is formed on a non-magnetic supporting body and a magnetic layer containing an organic lubricant is formed on the metal thin film.
In the above method, the recording medium may be a metal thin film optical recording medium in which an optical recording layer is formed on a non-magnetic supporting body and an organic thin film containing an organic lubricant is formed on the surface of the optical recording layer.
In the above method, an infrared light ray having a wavelength ranging from 2 xcexcm to 20 xcexcm may be made incident on the prism.
In the above method, the semi-spherical prism may have a refractive-index ranging from 2.0 to 4.0.
According to the analysis method of the present invention, the contact pressure applied from the surface of a sample during analysis to the bottom surface of the semi-spherical prism by the contact pressure control means is preferably in a range of 10 kgf/cm2 or less.
The reason why an infrared light ray is made incident on the prism in the state in which the contact pressure is kept at a value in the range 10 kgf/cm2 or less is for uniformly keeping the press-contact state between the surface of a sample and the bottom surface of the prism over the entire contact area, thereby performing high accurate analysis of the sample at a desired surface position and also obtaining an analysis result with a good repeatability. Additionally, in the case where a recording medium such as a floppy disk, a magnetic tape, a magnetic disk or an optical disk is taken as a sample, if the contact pressure is selected to be more than 10 kgf/cm2, the sample may be broken and thereby it is impossible to analyze the sample.
The above contact pressure control means preferably includes a presser metal, a pressing mechanism for bringing the presser metal into press-contact with the surface of a sample, a pressure detecting mechanism for detecting the contact pressure between the surface of the sample and the bottom surface of the prism, and a control mechanism for controlling the contact pressure in a specific range by suitably moving the presser metal by means of the pressing mechanism on the basis of detection data obtained by the pressure detecting mechanism. To be more specific, the presser metal is brought into press-contact with the surface of the sample by a spring or a hydraulic mechanism; the contact pressure is detected by a sensor such as a piezoelectric element connected to the control mechanism; and if the contact pressure is out of the above specific range, the presser metal is suitably moved by operating the pressing mechanism on the basis of a signal supplied from the control mechanism.
Examples of high density recording media capable of being analyzed according to the present invention may include (1) a coating type magnetic recording medium in which a magnetic paint mainly containing a binder and a ferromagnetic powder and additionally containing an organic lubricant is applied on a non-magnetic supporting body to form a magnetic layer; (2) a metal thin film type magnetic recording medium in which a metal thin film is formed on a non-magnetic supporting body and a magnetic layer containing an organic lubricant is formed on the metal thin film; and (3) a metal thin film type optical recording medium in which an optical recording layer is formed on a non-magnetic supporting body and an organic thin film containing an organic lubricant is formed on the surface of the optical recording layer.
Concretely, a magnetic tape (audio tape or video tape), a floppy disk, an optical disk (magneto-optical type or phase change type), and a hard disk are taken as the above high density recording media.
That is to say, according to the present invention, it is possible to simply, accurately perform at least one of qualitative analysis and quantitative analysis of an organic material, particularly an organic lubricant in or on the above high density recording medium. The lubricant on the recording medium means a lubricant present on the uppermost surface, opposed to the supporting body, of the recording medium, while the lubricant in the recording medium means a lubricant contained in the recording medium, that is, present in a layer between the surface of the supporting body and the uppermost surface of the recording medium. It should be noted that in the following description, the organic lubricant and the recording medium are sometimes referred to simply as xe2x80x9clubricantxe2x80x9d and xe2x80x9cmediumxe2x80x9d, respectively.
In the analysis method of a high density recording medium according to the present invention, the surface of a sample is brought into press-contact with the bottom surface (smooth plane) of the semi-spherical prism at a specific contact pressure; an infrared light ray having a wavelength ranging from 1 xcexcm to 20 xcexcm is made incident on the spherical plane of the semi-spherical prism (hereinafter, sometimes referred to simply as a xe2x80x9cprismxe2x80x9d); the spectrum of an organic matter in the uppermost surface layer portion (depth: 100 nm to several nm) of the sample is obtained by an evanescent wave leaked from inner reflection in the prism; and the spectrum is analyzed by using a Fourier transformer. The prism is made from a crystal which is transparent for infrared light rays and has a refractive index being as high as possible, for example, a crystal of germanium (Ge) or silicon (Si).
In the ordinary high sensitivity reflected infrared absorption spectroscopy, unless the reflectance of the surface of the sample is very high, light incident from a light source is absorbed in a sample, thereby making it impossible to attain satisfactory measurement. For a metal thin film type magnetic recording medium, a coating type magnetic recording medium, and an optical recording medium, since the reflectance of the surface of the medium is low, it is impossible to analyze a trace of lubricant on and in the medium by the high sensitivity reflected infrared spectroscopy.
To be more specific, in the high sensitivity reflected infrared absorption spectroscopy, analysis is performed by making a light ray incident on the surface of a sample at an angle of about 80xc2x0 with respect to the normal line of the surface of the sample, and allowing the light ray to be reflected from the surface of the sample at one time. Such a spectroscopy is generally suitable for analysis of an organic matter on the surface of a metal underlying film having a high reflectance, and is effective for analysis of an organic matter on a hard disk. However, since the reflectance of a recording medium such as a magnetic tape or a floppy disk is generally very low, it is impossible to analyze an organic matter on and in the recording medium. On the contrary, it is possible to accurately analyze an organic matter on and in any sample irrespective of the reflectance of the sample.
In an ATR method (attenuated reflection method utilizing multi-reflection) based on a general internally reflected infrared absorption spectroscopy, samples are overlapped on upper and lower surfaces of a plate-like prism; a packing and fastening plate are overlapped on the back surface of each sample; the samples and the prism are fastened with a bolt and a nut; and the samples thus assembled to the prism are set in a measuring apparatus for analysis. In this method, since fine adjustment is required to uniformly keep the press-contact state between the plate-like prism and the surface of the sample over the contact area, it is very difficult to perform accurate analysis. Further, if the amount of an object to be measured differs depending on the position on the surface of the sample, only an average value of the amounts of the object in a wide range on the sample can be obtained. In the case of adopting the ATR method, the concentration distribution of a lubricant at a micro-region (having a radius of 1 mm or less) cannot be obtained, unlike the present invention.
On the contrary, according to the analysis method of the present invention, since the semi-spherical prism is used and the contact pressure between the surface of a sample and the bottom surface of the prism is set in a specific range, the press-contact state can be uniformly kept in a wide range, with a result that an infrared light ray made incident on the prism can be simply, certainly converged at a specific position on the surface of the sample. As a result, it is possible to accurately perform qualitative analysis and quantitative analysis of a trace of lubricant present on and in the medium and to obtain the concentration of the lubricant at a micro-region (having a radius of 1 mm or less) at a very high sensitivity (that is, high S/N ratio).
From the examination performed by the present inventors, it is confirmed that in the case of analyzing a lubricant on and in a recording medium according to the present invention, to perform accurate analysis with a good repeatability, a difference in contact pressure applied from the surface of a sample to the bottom surface of the prism between two of the analysis operations is required to be in a range of several ten mgf/cm2 or less, and it can be controlled in a range of several mgf/cm2 or less by the contact pressure control means.
In the analysis method of the present invention, an infrared light ray having a wavelength ranging from 2 xcexcm to 20 xcexcm is used. The reason for this is that organic materials have absorption characteristics over a wide infrared light range, and most of organic materials absorb an infrared light ray having a wavelength ranging from 2 xcexcm to 20 xcexcm.
To accurately analyze a sample in a depth range from the uppermost surface to 1-2 xcexcm, the refractive index of the semi-spherical prism may be in a range of 1.5 to 5.0, preferably, 2.0 to 4.5. According to the present invention, the use of the prism having a larger refractive index is effective to analyze the uppermost surface of a sample, and the use of the prism having a smaller refractive index make it difficult to analyze the uppermost surface of the sample because of permeation of an infrared light ray to a deeper point in the sample.
To be more specific, according to the analysis method of the present invention, when a light ray is totally reflected at the interface between the prism and the surface of a sample, an evanescent wave occurs from the surface of the prism and permeates in the surface of the sample, with a result that information only from the uppermost surface of the sample can be obtained. If the refractive index of the prism is small (for example, 0.2), the above permeation depth becomes several xcexcm or more, therefore it is difficult to analyze the uppermost surface of the sample or its directly underlying portion (equivalent to a magnetic layer of a magnetic recording medium). The prism having a refractive index ranging from 2.0 to 4.5 is readily available and is effective to accurately analyze the uppermost surface of the sample and its directly underlying portion. The prism which is transparent for infrared light rays and has a refractive index of more than 4.5 is not readily available.
The present invention can be configured such that not only a lubricant on the uppermost surface of a medium but also an organic material in the medium can be analyzed. The reason for this is that an organic material, particularly a lubricant in the recording medium exerts a large effect on the reliability of the medium, and even for the same total amount of the lubricant on and in the medium, the reliability of the medium largely differs depending on the existing state of the lubricant in the medium (concentration distribution in the depth direction and the concentration on the surface). The accurate analysis of an organic material in a medium, which has been not achieved by the related art method, can be achieved by the present invention, and therefore, the present invention has an extremely important technical significance.
Since the incident angle variable optical system of the present invention is separated from the sample mounting portion by means of the semi-spherical prism, only the optical system can be enclosed, to facilitate the operation such as exchange of a sample. Also, since the optical system is enclosed, it is possible to prevent, upon exchange of a sample, the permeation of carbon dioxide or moisture in the optical path of the optical system and hence to suppress noise due to carbon dioxide or moisture, and also to eliminate the necessity of taking an excessive waiting time for substituting, after exchange of the sample, the interior of a sample chamber for nitrogen gas or the like for removing carbon dioxide or moisture.